The field of the present invention is electronic test systems. More particularly, the present invention relates to a cable test system comprising a tone generator and a tone probe.
The tremendous growth in communications systems has dramatically increased the complexities of maintaining cabling systems within a building or a business campus. Indeed, with the proliferation of phone and computer cabling, businesses and even individuals spend considerable time and resource installing, testing, and maintaining cabling systems.
In a typical cabling installation, wiring ports or jacks are provided at wall outlets throughout a building. Cables run from each of the port outlets to a central location, such as a network closet. In the network closet, each of the incoming cables is connected to an appropriate device, such as a phone panel or a network hub, router, or switch. Other connections are provided from the network closet to larger voice or data networks. Even a modest cabling installation will have several network closets or other locations to concentrate cable access.
A typical network closet for even a moderately sized business may contain hundreds, if not thousands of incoming cables. During initial installation, for example, generally one set of technicians will route the cables from the wall port, through the building infrastructure, and to the network cabinet. Another set of technicians typically completes the physical connections. In this regard the technicians making the physical connections may be presented with a maze of cables and must determine which cable in the network closet is routed to each of the physical wall outlets.
To assist in identifying cables, cable testing systems have been developed. In the known cable testing system, a tone generator is coupled to a cable at a particular wall outlet position. The tone generator applies a signal in the audio frequency, typically about 1 KHz, to the cable. A technician in the network closet uses a tone probe to search for the cable transmitting the tone signal. The tone probe has a probe tip which the technician runs adjacent to each of the cables. As the tone probe begins detecting the tone signal, the tone signal is amplified and broadcast on a speaker. For example, if the tone generator applies a 1 KHz tone signal to the cable, the technician will hear a 1 KHz audio signal as the probe tip detects the tone signal.
As the tone probe is brought nearer the cable having the tone signal, the output from the speaker will become louder, thereby informing the technician which cable actually carries the tone signal. In this regard the technician in the network closet is able to detect which of a multitude of cables is the cable connected to the point of interest. To assist in identifying a particular cable, some known tone generators produce a tone signal with a varying frequency. The changes in frequency cause the tone probe to broadcast a siren-like sound.
In another use of the known cable testing system, the tone generator/tone probe combination may be used to find physical breaks in a cable. For example, if a particular run of cable is suspected of having a physical break, the tone generator once again could be coupled to the wall outlet at the port. The tone probe may then be moved along the cable path until the tone probe can no longer detect the tone signal. Provided the tone probe has sufficient sensitivity, the place where the tone probe loses the tone signal is likely to be where there is a physical disruption to the cable. Often, such a physical disruption may have caused by a nail or screw inadvertently driven through the cable. The cable test system thereby enables non-intrusive break detection for cables, avoiding the time and expense of rerouting cables or significant demolition of walls or other structures.
The typical known tone generator provides a tone signal in the audible band, generally around 1 KHz. Since the known tone probe may be used on voice phone lines, the tone generators provide a signal within the expected frequency band of the phone line. Due to the electrical sensitivities of devices which may be coupled to the cable, and for safety reasons the power applied to the tone signal is quite limited. Accordingly, the tone probe must be highly sensitive to detect the presence of the tone signal. The in-band tone signal, when detected and amplified, provides an audible signal readily perceived by most humans.
Known tone probes are constructed to detect signals at about the tone signal frequency. In order to increase the likelihood of detecting a signal, the typical tone probe detects a fairly wide range of frequencies. For example, if the tone generator outputs a signal at about 1 KHz, then the tone probe may be sensitive and respond to signals within 100 or more Hz above or below that value. The wide sensitivity range is useful as the initial frequency generated by the tone generator may not be very accurate, and the frequency of the tone signal may vary widely over time due to environmental or other conditions. Further, a single tone probe may be used to detect tone signals generated by several tone generators, and the frequency may vary considerably between tone generators.
Also, since the tone signal radiating from the test cable is very small, the signal detected by the probe tip is typically greatly amplified. In this regard, the known tone probe uses a high gain amplifier to amplify signals near the expected tone frequency. The tone probe may use filters to remove some noise, and then broadcast the amplified signals on a speaker.
Unfortunately, tone probes are known to also detect and react to a wide range of spurious signals. For example, the probe may pick up noise from fluorescent lights, computer monitors, or other signals being transmitted on the test cable. Since a tone probe cannot distinguish the source of these signals, the probe either indicates the false presence of the tone generator, or presents an obnoxious level of noise.
Further, when the tone probe begins detecting the tone signal, the speaker begins amplifying the signal and broadcasting the amplified signal to the operator. Unfortunately, the broadcast signal and electronics driving the speaker may cause feedback into the probe tip. Such feedback may cause an annoying runaway feedback problem, and if not stopped in time may damage the tone probe. Due to such feedback problems, operators often turn the volume down on the tone probe in operation. In such a case, the operator may then be unaware of the presence of a tone signal because the volume is set too low.
It has proven particularly difficult to identify the terminus points for Ethernet networking cables. The problem is especially difficult for existing cabled environments. For example, a computer may be connected to an Ethernet port in an office wall. The cable is routed through the office walls to a network cabinet, where the cable is physically coupled to a hub, router, or switch. Even in a moderately sized company, a network cabinet may have dozens or even hundreds of Ethernet cables connected into such network devices. Typically, each network device has a link LED showing that the cable has established communication between the network device and the client device, such as the personal computer. However, when the technician desires to identify a specific cable, it is typically a time consuming and frustrating job to find the particular device and port attachment for a specific cable.
Accordingly, there is a need for a cable test system capable of more accurately and efficiently identifying cables and cable connections.
To overcome the deficiencies as described above, and to provide a cable test system with improved accuracy and efficiency, a new tone generator and tone probe is described. Briefly, the tone generator uses a highly accurate frequency signal to generate an accurate and stable tone signal. A cadence pattern may be used to output the tone signal onto a test cable in an easily distinguishable pattern. In a specific arrangement, the tone signal may be selectively output at an in-band frequency within the frequency range of information signals on the cable, or an out-band frequency outside the frequency range of information signals on the cable.
A corresponding tone probe may be used to detect the tone signal. As the tone signal""s frequency is highly accurate and stable, the tone probe uses a high-Q bandpass filter to reject all but the expected frequency of the tone signal. In a specific example, the bandpass filter is implemented digitally to efficiently reject all but the desired narrowband frequency. The signal passing the bandpass filter is proportional to the detected tone signal, so may be used to drive an LED array to display the relative strength of the detected tone signal. The tone probe also includes an audio signal generator, which generates an audio signal unrelated to the frequency of the tone signal. The generated audio signal is modulated responsive to the signal from the bandpass filter, and then driven through a speaker. Accordingly, the tone probe provides an audible signal proportional to the strength of the tone signal, but is unrelated in frequency.
Advantageously, the tone generator and tone probe cooperate to provide a cable testing system having exceptional accuracy, ease of use, and efficiency. For example, when the tone generator is used to generate an out-band tone signal, the tone signal enables test and detection without interrupting in-band communication and signals. In such a manner, the out-band toning capability acts as a non-intrusive test for a cable. Also, since the tone generator provides a tone signal with a highly stable and accurate frequency, the tone probe may be constructed with a very high-Q bandpass filter, enabling excellent noise rejection. Further, since the sound broadcast from the tone probe has a frequency unrelated to the detected tone probe frequency, feedback and other undesirable effects are eliminated or substantially reduced.